The present invention relates to the aerodynamic configuration of an airplane airframe. Conventionally, and with rare exceptions (primary among which is the "flying wing"), airplanes consist of a fuselage, wings attached thereto and an empennage.
It has long been recognized that in producing lift and propelling an airplane through the air, certain drag forces are created. As the speed of an aircraft increases, the magnitude of the drag forces increases enormously. Drag is composed primarily of two components: induced drag and parasite drag. Parasite drag is caused by factors such as skin friction and airstream disturbing forms, for example, antennas, cowl openings and landing gear and airflow interference between components of the airframe, such as at the junction of wing and fuselage or fuselage and tail. Parasite drag is a function of air speed, i.e., increasing as the square of the air speed. Induced drag, on the other hand, varies inversely with air speed. In order to overcome the increased total drag, due primarily to greatly increased drag encountered at high speeds, greater power is required. These increased power requirements necessitate larger, more powerful engines which, in turn, require the carrying of increased quantities of fuel. The larger fuel loads also increase the gross weight of the aircraft thereby making further demands upon the power supply.
Modern aircraft design efforts have, therefore, concentrated very heavily upon minimizing drag. One of the areas on an airplane long known to cause drag problems has been the intersection between the wing and the fuselage. Among other things, the discontinuity at that point tends to cause turbulence and drag. One attempt to eliminate or at least minimize the turbulence generated at this intersection has been to flare the wing root so that the transition from fuselage to wing, particularly along the leading edge of the wing, is less abrupt. See, for example, Brownell, U.S. Pat. No. 2,927,749.
It has also been found that turbulence is created at the wing tips, in the form of wing tip vortices. Since, in flight, the air pressure below the wing is greater than that found above the wing (the Bernoulli Principle), air at the wing tip tends to flow from the high pressure to the low pressure zone. Thus, in addition to longitudinal flow of air from the leading to the trailing edge of the wing, there is also a component of lateral flow. It has been found that this lateral flow and the wing tip vortices are responsible for a significant amount of the overall drag of the aircraft in flight. This is of particular importance for aircraft which cruise near or above trans-sonic speeds.
One attempt to minimize the problems created by wing tip vortices has been the development of "winglets". Reference to such appendages can be found, for example, in various issues of Aviation Week & Space Technology, including Oct. 3, 1977 (page 16), Oct. 10, 1977 (cover), Mar. 6, 1978 (pages 9 and 14), and Mar. 16, 1978 (page 13). A discussion of winglets can also found in the article beginning on page 35 of the Sept. 1978 issue of PILOT, the official publication of the Aircraft Owners and Pilots Association (AOPA). Another approach to solving the wing tip vortexing problem has been to use a swept-forward wing. The span-wise flow along such wings tends to be toward the fuselage, not toward the wing tip.
In aircraft design, numerous approaches have been made to maximize lift. Toward this end, some designs have incorporated lifting body fuselages. As used herein, a lifting body fuselage is one that has any airfoil shape with a low aspect ratio (the ratio of span to chord) relative to those characteristic of conventional wings. Examples of lifting bodies will be found in U.S. Pat. Nos. 1,928,317, 2,864,567, 2,989,269, 3,576,300, 3,684,217, 3,743,218 and 3,869,102.
When an airplane moves through the air, the displacement of air by the various components causes increased pressure in the regions immediately adjacent the airplane skin. Thus, the static air pressure immediately above the wing is greater than the static air pressure at some distance from the surface where the air remains undisturbed. This also holds true around the fuselage. It can therefore be seen that at the junction of the wing and the fuselage there is a convergence of two relatively high pressure areas. This convergence of the two zones tends to cause turbulence and increased drag over the entire length of the junction. In addition, the junction tends to disturb smooth airflow which also leads to turbulence.
In my invention I substantially reduce this turbulence and the attendant drag by separating the wing from the fuselage. The wing is connected to the fuselage through an intervening airfoil-shaped spar of substantially decreased cross sectional area from that of the adjacent wing section. Preferably, the spar should be symmetrical about its horizontal center plane. The two high pressure zones caused by the displacement of air by the wing and by the fuselage are separated by use of the spar and the turbulence caused by their convergence substantially reduced. Additionally, due to the shorter chord length of the spar the junction between spar and fuselage has been foreshortened resulting in a shorter zone of airflow disturbance. In my preferred embodiment, airstream disturbance is further reduced by orienting the spars so as to provide 0.degree. angle of incidence.
There are examples in the prior art of airframes wherein the wings have been separated from the fuselage. See, for example, U.S. Pat. Nos. 1,779,005 (Lanier), 1,913,809 (Lanier) and 2,186,558 (Rousnet). The structures shown and the purposes to be served by the structures shown in those patents are, however, quite different from those contemplated by the instant invention. For example, in my invention I connect the wing to the fuselage through a single airfoil-shaped spar to reduce turbulence and drag. In the Lanier patents no consideration appears to have been given to reducing turbulence. This is evident from the fact that the wings are joined to the fuselage by use of multiple spars, none of which appear to have an airfoil shape. Such structure tends to produce more, not less, turbulence. In the the '558 patent, while a discontinuity is provided, it is to enable the wing to pivot when acted upon by certain aerodynamic forces. There is no teaching that the separation would serve any of the purposes contemplated by the instant invention.
Another reference of interest is U.S. Pat. No. 1,965,790 which shows a wing having a reduced chord and thickness immediately adjacent the fuselage. This is provided, however, to increase the pilot's view both forward and down, not to serve any aerodynamic function.
Other patents which are of only peripheral interest in this connection are U.S. Pat. Nos. 3,123,321 and 2,065,401.
None of the above references show the wing/spar/fuselage structure contemplated by the instant invention nor would the structures shown in any of those, either alone or in combination, serve the purposes which my invention serve.
My invention also contemplates use of winglets at the wing tips to minimize the generation of vortices and lateral flow of air toward the end of the wing. Unlike previous designs, however, my winglets can be moved in flight. In cruise configuration they serve primarily to minimize wing tip vortices without substantially increasing induced drag. The geometry and positioning of these winglets in cruise are selected to minimize parasite drag as well. In the landing configuration they are substantially horizontal and become an extension of the wing, thereby providing increased wing area and decreased wing loading.
The Feb. 19, 1979 issue of Aviation Week & Space Technology shows a picture of a model airplane with what appear to be variable wing tips. It is said that the model "has variable geometry anhedral to explore means of aleviating excessively high dihedral." Thus, it would appear that the purpose these wing tips were designed to serve is quite different from the purpose served by my moveable winglets. Moreover, it is not even clear from the limited description in Aviation Week & Space Technology that the variable wing tips are moveable in flight, as opposed to being variable from one wind tunnel test to another.
Since the wing in my invention is separated from the fuselage, lateral flow inwardly along the wing near its wing root would be likely to occur for the same reasons that lateral flow occurs at the wing tip. I have therefore provided wing fences at the fuselage end of the wing, where the wing joins the spar.
My design also contemplates a lifting body fuselage. Once again, however, the differential pressure between the air above the lifting body and that below, along the longitudinal edges of the lifting body, tend to produce votices and turbulence similar to that found at wing tips. I have therefore provided longitudinal splines along the lifting body to minimize these effects and the attendant drag. The angle at which these splines join the fuselage can be made variable, they can be made extenable out from the fuselage and they can, in addition, incorporate longitudinal flaps. It is anticipated that full extension of the splines and flaps in the landing configuration will provide substantially increased lift at that critical stage in the flight. Moreover, the turned down flaps and splines in the landing configuration tend to inhibit vortexing, an increasingly important feature as the angle of attack of the lifting body becomes more pronounced. These variable splines and/or flaps can also be employed singly or in unison during normal flight operations to improve the maneuverability envelope.
While each of the above features can be used independently of the others, the most efficient design would incorporate all of them. In that preferred embodiment one would achieve the cooperative benefits of reduced drag during cruise coupled with increased lift.
The airframe design described herein incorporates the above features to produce an airplane having substantially improved aerodynamic characteristics over airplanes of the prior art. Drag is reduced, particularly in the high sub-sonic, transsonic and supersonic ranges and lift is increased both in normal flight, including climb, descent and cruise, and especially during landing.